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74LS138

Fairchild Semiconductor
Part Number 74LS138
Manufacturer Fairchild Semiconductor
Published Mar 23, 2005
Description Decoder/Demultiplexer
Detailed Description DM74LS138 • DM74LS139 Decoder/Demultiplexer August 1986 Revised March 2000 DM74LS138 • DM74LS139 Decoder/Demultiplexer...
Datasheet PDF File 74LS138 PDF File

74LS138
74LS138


Overview
DM74LS138 • DM74LS139 Decoder/Demultiplexer August 1986 Revised March 2000 DM74LS138 • DM74LS139 Decoder/Demultiplexer General Description These Schottky-clamped circuits are designed to be used in high-performance memory-decoding or data-routing applications, requiring very short propagation delay times.
In high-performance memory systems these decoders can be used to minimize the effects of system decoding.
When used with high-speed memories, the delay times of these decoders are usually less than the typical access time of the memory.
This means that the effective system delay introduced by the decoder is negligible.
The DM74LS138 decodes one-of-eight lines, based upon the conditions at the three binary select inputs and the three enable inputs.
Two active-low and one active-high enable inputs reduce the need for external gates or inverters when expanding.
A 24-line decoder can be implemented with no external inverters, and a 32-line decoder requires only one inverter.
An enable input can be used as a data input for demultiplexing applications.
The DM74LS139 comprises two separate two-line-to-fourline decoders in a single package.
The active-low enable input can be used as a data line in demultiplexing applications.
All of these decoders/demultiplexers feature fully buffered inputs, presenting only one normalized load to its driving circuit.
All inputs are clamped with high-performance Schottky diodes to suppress line-ringing and simplify system design.
Features s Designed specifically for high speed: Memory decoders Data transmission systems s DM74LS138 3-to-8-line decoders incorporates 3 enable inputs to simplify cascading and/or data reception s DM74LS139 contains two fully independent 2-to-4-line decoders/demultiplexers s Schottky clamped for high performance s Typical propagation delay (3 levels of logic) DM74LS138 DM74LS139 DM74LS138 DM74LS139 21 ns 21 ns 32 mW 34 mW s Typical power dissipation Ordering Code: Order Number DM74LS138M DM74LS138SJ DM74LS1...


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